US 7150780 B2
An electrostatic air cleaning device includes an array of electrodes. The electrodes include corona electrodes connected to a suitable source of high voltage so as to generate a corona discharge. Laterally displaced collecting electrodes include one or more bulges that have aerodynamic frontal “upwind” surfaces and airflow disrupting tailing edges downwind that create quite zones for the collection of particulates removed from the air. The bulges may be formed as rounded leading edges on the collecting electrodes and/or as ramped surfaces located, for example, along a midsection of the electrodes. Repelling electrodes positioned between pairs of the collecting electrodes may include similar bulges such as cylindrical or semi-cylindrical leading and/or trailing edges.
1. An electrostatic air cleaning device comprising:
a plurality of corona electrodes having respective ionizing edges;
at least one complementary electrode having a substantially planar portion and a protuberant portion extending outwardly in a lateral direction substantially perpendicular to a desired fluid-flow-direction; and
at least one repelling electrode having a substantially planar portion and at least one protuberant portion extending outwardly in a lateral direction substantially perpendicular to said desired fluid-flow direction.
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27. An electrostatic air cleaning device comprising:
a plurality of corona electrodes having respective ionizing edges; and
at least one collecting electrode having a substantially planar portion and a raised trap portion formed on a midsection of said collecting electrode and extending outwardly above a height of said substantially planar portion for a distance greater than a nominal thickness of said planar portion; and
a repelling electrode positioned intermediate adjacent pairs of said collecting electrodes; and
a repelling electrode positioned intermediate adjacent pairs of said collecting electrodes.
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33. An electrostatic air cleaning device comprising:
a plural first number of corona electrodes having respective ionizing edges;
a plural second number of collecting electrodes spaced apart from (i) each other in a lateral direction and (ii) said corona electrodes in a longitudinal direction;
a plural third number of repelling electrodes that are spaced apart and substantially parallel to the collecting electrodes; and
an electrical power source connected to supply said corona, collecting and repelling electrodes with an operating voltage to produce a high intensity electric field in an inter-electrode space between said corona, collecting and repelling electrodes,
said collecting and repelling electrodes each having a profile including bulges causing a turbulent fluid flow through an inter-electrode passage between adjacent ones of said collecting and repelling electrodes.
34. An electrostatic air cleaning device according to
wherein a leading edge of each of said collecting electrodes has a rounded bulge.
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wherein a leading edge of each of said collecting electrodes has a half-rounded bulge.
37. An electrostatic air cleaning device according to
wherein an edge of an electrode that is positioned closest to an air passage outlet has a greatest electrical potential difference with respect to the corona electrode.
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44. An electrostatic air cleaning device comprising:
a plurality of corona electrodes having respective ionizing edges;
at least one complementary electrode configured to impart motion to a fluid in a desired fluid-flow direction, said complementary electrode having a substantially planar portion and a protuberant portion extending outwardly in a lateral direction substantially perpendicular to said desired fluid-flow direction; and
at least one repelling electrode having a substantially planar portion and at least one protuberant portion extending outwardly in a lateral direction substantially perpendicular to said desired fluid flow direction.
The instant application is related to U.S. patent application Ser. No. 09/419,720 filed Oct. 14, 1999 and entitled Electrostatic Fluid Accelerator, now U.S. Pat. No. 6,504,308; U.S. patent application Ser. No. 10/187,983 filed Jul. 3, 2002 and entitled Spark Management And Device; U.S. patent application Ser. No. 10/175,947 filed Jun. 21, 2002 and entitled Method Of And Apparatus For Electrostatic Fluid Acceleration Control Of A Fluid Flow and the Continuation-In-Part thereof, U.S. patent application Ser. No. 10/735,302 filed Dec. 15, 2003 of the same title; U.S. patent application Ser. No. 10/188,069 filed Jul. 3, 2002 and entitled Electrostatic Fluid Accelerator For And A Method Of Controlling Fluid Flow; U.S. patent application Ser. No. 10/352,193 filed Jan. 28, 2003 and entitled An Electroststic Fluid Accelerator For Controlling Fluid Flow; U.S. patent application Ser. No. 10/295,869 filed Nov. 18, 2002 and entitled Electrostatic Fluid Accelerator; U.S. patent application Ser. No. 10/724,707 filed Dec. 2, 2003 and entitled Corona Discharge Electrode And Method Of Operating The Same, each of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The invention relates to a device for electrostatic air cleaning. The device is based on the corona discharge and ions acceleration along with dust particles charging and collecting them on the oppositely charged electrodes.
2. Description of the Related Art
A number of patents (see, e.g., U.S. Pat. Nos. 4,689,056 and 5,055,118) describe electrostatic air cleaning devices that including (i) ion and resultant air acceleration generated by a corona discharge method and device coupled with (ii) charging and collection of airborne particulates, such as dust. These corona discharge devices apply a high voltage potential between corona (discharge) electrodes and collecting (or accelerating) electrodes to create a high intensity electric field and generate a corona discharge in a vicinity of the corona electrodes. Collisions between the ions generated by the corona and surrounding air molecules transfer the momentum of the ions to the air thereby inducing a corresponding movement of the air to achieve an overall movement in a desired air flow direction. U.S. Pat. No. 4,689,056 describes the air cleaner of the ionic wind type including corona electrodes constituting a dust collecting arrangement having the collecting electrodes and repelling electrodes alternately arranged downstream of said corona electrode. A high voltage (e.g., 10–25 kV) is supplied by a power source between the corona electrodes and the collecting electrodes to generate an ionic wind in a direction from the corona electrodes to the collecting electrode. As particulates present in the air pass through the corona discharge, a charge corresponding to the polarity of the corona electrodes is accumulated on these particles such that they are attracted to and accumulate on the oppositely-charged collecting electrodes. Charging and collecting of the particles effectively separates-out particulates such as dust from fluids such as air as it passes through the downstream array of collecting electrodes. Typically, the corona electrodes are supplied with a high negative or positive electric potential while the collecting electrodes are maintained at a ground potential (i.e., positive or negative with respect to the corona electrodes) and the repelling electrodes are maintained at a different potential with respect to the collecting electrodes, e.g., an intermediate voltage level. A similar arrangement is described in U.S. Pat. No. 5,055,118.
These and similar arrangements are capable of simultaneous air movement and dust collection. However, such electrostatic air cleaners have a comparatively low dust collecting efficiency that ranges between 25–90% removal of dust from the air (i.e., “cleaning efficiency”). In contrast, modern technology often requires a higher level of cleaning efficiency, typically in the vicinity of 99.97% for the removal of dust particles with diameter of 0.3 μm and larger. Therefore state-of-the-art electrostatic air cleaners can not compete with HEPA (high efficiency particulate air) filtration-type filters that, according to DOE-STD-3020-97, must meet such cleaning efficiency.
Accordingly, a need exists for an electrostatic fluid precipitator and, more particularly, an air cleaning device that is efficient at the removal of particulates present in the air.
One cause for the relatively poor collecting efficiency of electrostatic devices is a general failure to consider movement of the charged particulates and their trajectory or path being charged in the area of the corona discharge. Thus, a dust particle receives some charge as it passes near the corona electrode. The now charged particle is propelled from the corona electrodes toward and between the collecting and repelling electrodes. The electric potential difference between these electrodes plates creates a strong electric field that pushes the charged particles toward the collecting electrode. The charged dust particles then settle and remain on the collecting electrode plate.
A charged particle is attracted to the collecting electrode with a force which is proportional to the electric field strength between the collecting and repelling electrodes' plates:
Another factor limiting particulate removal (e.g., air cleaning) efficiency is caused by the existence of a laminar air flow in-between the collecting and repelling electrodes, this type of flow limiting the speed of charged particle movement toward the plates of the collecting electrodes.
Still another factor leading to cleaning inefficiency is the tendency of particulates to dislodge and disperse after initially settling on the collecting electrodes. Once the particles come into contact with the collecting electrode, their charges dissipate so that there is no longer any electrostatic attractive force causing the particles to adhere to the electrode. Absent this electrostatic adhesion, the surrounding airflow tends to dislodge the particles, returning them to the air (or other fluid being transported) as the air flow through and transits the electrode array.
Embodiments of the invention address several deficiencies in the prior art such as: poor collecting ability, low electric field strength, charged particles trajectory and resettling of particles back onto the collecting electrodes. According to one embodiment, the collecting and repelling electrodes have a profile and overall shape that causes additional air movement to be generated in a direction toward the collecting electrodes. This diversion of the air flow is achieved by altering the profile from the typical flat, planar shape and profile with the insertion or incorporation of bulges or ridges.
Note that, as used herein and unless otherwise specified or apparent from context of usage, the terms “bulge”, “projection”, “protuberance”, “protrusion” and “ridge” include extensions beyond a normal line or surface defined by a major surface of a structure. Thus, in the present case, these terms include, but are not limited to, structures that are either (i) contiguous sheet-like structures of substantially uniform thickness formed to include raised portions that are not coplanar with, and extend beyond, a predominant plane of the sheet such as that defined by a major surface of the sheet (e.g., a “skeletonized” structure), and (ii) compound or composite structures of varying thickness including (a) a sheet-like planar portion of substantially uniform thickness defining a predominant plane and (b) one or more “thicker” portions extending outward from the predominant plane (including structures formed integral with and/or on an underlying substrate such as lateral extensions of the planar portion).
According to one embodiment, the bulges or ridges run along a width of the electrodes, substantially transverse (i.e. orthogonal) to the overall airflow direction through the apparatus. The bulges protrude outwardly along a height direction of the electrodes. The bulges may include sheet-like material formed into a ridge or bulge and/or portions of increased electrode thickness. According to an embodiment of the invention, a leading edge of the bulge has a rounded, gradually increasing or sloped profile to minimize and/or avoid disturbance of the airflow (e.g., maintain and/or encourage a laminar flow), while a trailing portion or edge of the bulge disrupts airflow, encouraging airflow separation from the body of the electrode and inducing and/or generating a turbulent flow and/or vortices. The bulges may further create a downstream region of reduced air velocity and/or redirect airflow to enhance removal of dust and other particulates from and collection on the collecting electrodes and further retention thereof. The bulges are preferably located at the ends or edges of the electrodes to prevent a sharp increase of the electric field. Bulges may also be provided along central portions of the electrodes spaced apart from the leading edge.
In general, the bulges are shaped to provide a geometry that creates “traps” for particles. These traps should create minimum resistance for the primary airflow and, at the same time, a relatively low velocity zone on a planar portion of the collecting electrode immediately after (i.e., at a trailing edge or “downwind” of) the bulges.
Embodiments of the present invention provide an innovative solution to enhancing the air cleaning ability and efficiency of electrostatic fluid (including air) purifier apparatus and systems. The rounded bulges at the ends of the electrodes decrease the electric field around and in the vicinity of these edges while maintaining an electric potential difference and/or gradient between these electrodes at a maximum operational level without generating sparking or arcing. The bulges are also effective to make air movement turbulent. Contrary to prior teachings, a gentle but turbulent movement increases a time period during which a particular charged particle is present between the collecting and repelling electrodes. Increasing this time period enhances the probability that the particle will be trapped by and collect on the collecting electrodes. In particular, extending the time required for a charged particle to transit a region between the collecting electrodes (and repelling electrodes, if present) enhances the probability that the particle will move in sufficiently close proximity to be captured by the collecting electrodes.
The “traps” behind the bulges minimize air movement behind (i.e., immediately “downwind” of) the bulges to a substantially zero velocity and, in some situations, results in a reversal of airflow direction in a region of the trap. The reduced and/or reverse air velocity in the regions behind the traps results in those particles that settle in the trap not being disturbed by the primary or dominant airflow (i.e., the main airstream). Minimizing disturbance results in the particles being more likely to lodge in the trap area for some period of time until intentionally removed by an appropriate cleaning process.
The array of electrodes includes three groups: (i) a subarray of laterally spaced, wire-like corona electrodes 102 (two are shown) which array is longitudinally spaced from (ii) a subarray of laterally spaced, plate-like collecting electrodes 103 (three are shown) while (iii) a subarray of plate-like repelling electrodes 104 (two are shown) are located in-between of and laterally dispersed between collecting electrodes 103. A high voltage power supply (not shown) provides the electrical potential difference between corona electrodes 102 and collecting electrodes 103 so that a corona discharge is generated around corona electrodes 102. As a result, corona electrodes 102 generate ions that are accelerated toward collecting electrodes 103 thus causing the ambient air to move in an overall or predominant desired direction indicated by arrow 105. When air having entrained therein various types of particulates, such as dust (i.e., “dirty air”) enters the arrays from a device inlet portion (i.e., from the left as shown in
Corona electrodes 102, collecting electrodes 203 and repelling electrodes 204 are connected to an appropriate source of high voltages such as high voltage power supply 100 (
The arrangement of
Referring again to
Further improvements may be obtained by implementing different shapes of the collecting electrode such as the semi-cylindrical geometry shown in the
A skeletonized version of a collecting electrode is depicted in
An alternate configuration is depicted in
Another embodiment of the invention is depicted in
Quite zone 409 is formed in a region downwind or behind walls 416 by the redirection of airflow caused by dust trap 414 as air is relatively gently redirected along ramp portions 415. At the relatively abrupt transition of walls 416, a region of turbulent airflow is created. To affect turbulent airflow, walls 416 may be formed with a concave geometry within region 413.
While dust traps 414 are shown as a symmetrical wedge with opposing ramps located on either side of collecting electrodes 403, an asymmetrical construction may be implemented with a ramped portion located on only one surface. In addition, while only one dust trap is shown for ease of illustration, multiple dust traps may be incorporated including dust traps on alternating surfaces of each collecting electrode. Further, although the dust traps as shown shaped as wedges, other configuration may be used including, for example, semi-cylindrical geometries similar to that shown for leading edge bulges 407.
Dust traps may also be created by forming a uniform-thickness plate into a desired shape instead using a planar substrate having various structures formed thereon resulting in variations of a thickness of an electrode. For example, as shown in
A fully skeletonized version of a collecting electrode 403B is depicted in
Further improvements may be achieved by developing the surfaces of repelling electrodes 504 to cooperate with collecting electrodes 403 as depicted in
Bulges 507 serve two purposes. The bulges both create additional air turbulence and increase the electric field strength in the areas between bulges 414 of collecting electrodes 403. That increased electric field “pushes” charged particles toward the collecting electrodes 403 and increases the probability that particulates present in the air (e.g., dust) will settle and remain on the surfaces of collecting electrodes 403.
Some examples of other possible repelling electrodes structures are depicted in
Another configuration of repelling electrode is shown in
Apertures 619 further encourage turbulent airflow and otherwise enhance particulate removal. At the same time, this configuration avoids generation of an excessive electric field increase that might otherwise be caused by the proximity of the sharp edges of the bulges 414 to the repelling electrodes 604.
It should be noted that round or cylindrical shaped bulges 517 and 607 are located at the far upstream (leading edge) and downstream (trailing edge) ends of the repelling electrodes 504 and 604 respectively. This configuration reduces the probability of occurrence of an electrical breakdown between the edges of the repelling electrodes and the collecting electrodes, particularly in comparison with locating such bulges near a middle of the electrodes. Experimental data has shown that the potential difference between the repelling and collecting electrodes is a significant factor in maximizing device dust collection efficiency. The present configuration supports this requirement for maintaining a maximum potential difference between these groups of electrodes without fostering an electrical breakdown of the intervening fluid, e.g., arcing and/or sparking through the air.
It should also be noted that, in the embodiment of
Although certain embodiments of the present invention have been described with reference to the drawings, other embodiments and variations thereof fall within the scope of the invention. In addition, other modifications and improvements may be made and other features may be combined within the present disclosure. For example, the structures and methods detailed in U.S. patent application Ser. No. 10/724,707 filed Dec. 2, 2003 and entitled Corona Discharge Electrode And Method Of Operating The Same describes a construction of corona electrodes and method of and apparatus for rejuvenating the corona electrodes that may be combined within the spirit and scope of the present invention to provide further enhancements and features.
It should be noted and understood that all publications, patents and patent applications mentioned in this specification are indicative of the level of skill in the art to which the invention pertains. All publications, patents and patent applications are herein incorporated by reference to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference in its entirety.
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